Overview of GI Physiology Flashcards
What does the GI tract consist of and what separates it?
- mouth
- oesophagus
- stomach
- small intestine
- large intestine
- appendix
- rectum
- anus
- accessory organs
- separated by sphincters
- upper oesophageal sphincter
- lower oesophageal sphincter
- pyloric sphincter
- ileocal sphincter
- internal and external sphincters
Describe the splanchnic circulation
- blood from gut, spleen and pancreas flows through portal vein to liver
- liver filters blood through sinuses and it leaves through hepatic vein to vena cava
What is the role of splanchnic circulation?
- removal of bacteria/particulate matter that can enter the blood from the GI tract
- prevents direct transport of potentially harmful agents into body
What is the role of the villi in the intestines?
increases the surface area to allow for increased absorption
Describe the organisation of the GI tract from superficial to deep
- serosa
- longitudinal muscle
- myenteric (Auerbach’s plexus)
- circular muscle
- submucous muscle (longitudinal)
- submucosal (Meissner’s plexus)
- mucosa
all of GI tract except oesophagus and distal rectum which lacks serosa and mesentery
What are the main functions of GI tract motility?
- propel ingested food along entire length of GIT
- mixing and grinding contents of GIT
- aid absorption of nutrients and water
- clear the stomach and intestines of luminal contents
Describe the 2 main types of GIT motility
Fed state:
- peristalsis and mixing movements
- accounts for movement, mixing and absorption of food
Interdigestive state:
- also known as migrating motor complexes (MMCs)
- responsible for clearing the stomach and intestines of luminal contents
Describe the control of GIT motility
- extrinsic control: neural and hormonal
- intrinsic control: myogenic, neural and chemical
Where is the myenteric plexus found and what does it control?
- between circular and longitudinal muscle layers
- innervates both muscle layers
- motor control of GIT
Where is the submucosal plexus found and what does it control?
- between circular smooth muscle and mucosa
- innervates glandular epithelium, endocrine glands and blood vessels
- controls GIT secretion
Describe the extrinsic NS
- parasympathetic neurons are branches of vagus, pelvic and splanchnic nerves
- innervate neurons in myenteric plexus
- stimulate GIT motility and secretion
- sympathetic nerves originate from celiac, superior and inferior mesenteric and hypogastric plexuses
- terminate on enteric nerves, smooth muscles and mucosa
- inhibit GIT motility and secretion
Describe the properties of GI smooth muscle cells
- muscle fibres connected by gap junctions and focal adhestions
- actin and myosin filaments aligned diagonally along long axis of cells
- filaments anchored at dense bodies scattered throughout sarcoplasma
- contractile arrays anchored to sarcolemma by dense plaques
Describe the electrical activity of the GI smooth muscle
- stimulated by slow intrinsic electrical activity
- initiated by specialised area in stomach called Interstitial Cells of Cajal (ICC) - mainly due to opening of Ca2+ channels leading to influx of Ca2+
What is the relationship between slow waves and spike potentials?
the higher the slow wave potential, the greater the frequency of spike potentials
What are the 2 types of electrical activity in GI smooth muscle cells?
- slow waves (basal electrical rhythm) which are slow changes in resting membrane potential
- spike potentials which are true APs
